1. Field of the Invention
The invention is directed generally to heat pumps, and more specifically to a high pressure heat pump using carbon dioxide as the circulating fluid.
2. Description of Related Art
Heat pumps are well known in the art. A heat pump is simply a device for delivering heat or cooling to a system, whereas a refrigerator is a device for removing heat from a system. Thus, a refrigerator may be considered a type of heat pump. Throughout the application, the invention will be referred to as a heat pump with the understanding that the designation of refrigerator could be substituted without changing the operation of the device.
In absorption heat pumps, an absorbent such as water absorbs the refrigerant, typically ammonia, thus generating heat. When the combined solution is pressurized and heated further, the refrigerant is expelled. When the refrigerant is pre-cooled and expanded to a low pressure, it provides cooling. The low pressure refrigerant is then combined with the low pressure depleted solution to complete the cycle.
Many current absorption heat pump/refrigerators make use of either a water-ammonia couple, or a water-lithium bromide. These two absorption couples suffer from certain drawbacks. The water-ammonia couple raises security problems in view of the toxicity and flammability of ammonia, and LiBr is corrosive and very failure prone due to low pressure operation, i.e., small leaks create contamination. Moreover, the tendency to crystallize can be a clogging problem. Operating at very low pressures is often impossible due to the freezing of water. Other absorption processes have been proposed, but all involve working fluids that are toxic, flammable, ozone-depleting, or have high atmospheric green house effects. The art lacks an environmentally friendly and efficient cycle that uses a non-toxic, non-corrosive working fluid with a positive working pressure.
The present invention is a safe, environmentally friendly absorptive cooling/heating process. The process uses a carbon dioxide absorption cycle that utilizes a liquid, non-toxic absorbent such as alcohol, from which the carbon dioxide gas is absorbed. Only the carbon dioxide refrigerant is circulated to the evaporator and condenser heat exchangers, the components directly in contact with breathable air, thus avoiding the problem of alcohol""s flammability.